A perpendicular magnetic recording system has a stable recording state because adjacent magnetizations directed to an opposite direction, and the system is essentially suited to high-density recording. A perpendicular magnetic recording medium is composed of a structure of deposited layers primarily of a soft magnetic underlayer, a seed layer, an intermediate layer, and a magnetic recording layer. The soft magnetic underlayer has the roles of suppressing the spread of the magnetic field generated by a magnetic head and efficiently magnetizing the magnetic recording layer. The seed layer and the intermediate layer have the role of controlling the segregation of the oxide and the crystal orientation in the magnetic recording layer. Usually, a granular recording layer doped with an oxide such as SiO2 in a CoCrPt alloy is used in the magnetic recording layer. The magnetic cluster size of the magnetic recording layer is reduced by segregating the oxides at the magnetic grain boundaries in the surroundings of the magnetic grains formed by the CoCrPt alloy. To obtain good read-write performance, one condition is to reduce the magnetic cluster size.
To further improve the read-write performance and increase the recording density, the write-ability must be improved while maintaining or reducing the magnetic cluster size in the magnetic recording layer, and one way to improve write-ability is to reduce the distance between the soft magnetic underlayer and the magnetic head. As described above, the soft magnetic underlayer has the dual roles of preventing the spread of the magnetic flux generated by the writing head and assisting in writing to the magnetic recording layer. Therefore, by reducing the distance between these components, a steeper magnetic field gradient of the writing head and more efficient recording are possible.
To reduce the distance between the soft magnetic underlayer and the magnetic head, reduction of the flying distance of the magnetic head and decrease in the film thicknesses of the overcoat layer, the lubrication layer, the magnetic recording layer, and the intermediate layer are helpful. This reduction in the film thicknesses of the overcoat layer and the lubrication layer are limited from the perspective of reliability. Reducing the film thickness of the magnetic recording layer introduces the problems of degradation of thermal stability of the magnetization in the magnetic recording layer, an increase in noise, and degradation in the signal quality. Because the intermediate layer and the seed layer have the roles of controlling the crystal orientation and structure of the magnetic recording layer, there are limits to thinning the film thicknesses of the intermediate layer and the seed layer while maintaining the characteristics of the magnetic recording layer.
In another attempt to increase write-ability, a method has been proposed to effectively reduce the distance between the soil magnetic layer and the magnetic head by replacing the seed layer with a soft magnetic material, e.g., Japanese Unexamined Patent Application Publication Nos. 2003-123239, 2007-179598, and 2004-288348. In these examples, when replacing the seed layer with a soft magnetic material, it is difficult to improve the write-ability without degrading the magnetic characteristics such as the crystal orientation and magnetic cluster size of the magnetic recording layer.
Therefore, a method and system which can effectively improve write-ability while avoiding the problems seen in conventional methods would be very beneficial.